Bass Strait battlers

Location:	Deal Island is the largest of the Kent Group which comprises Tasmania's northernmost and most remote national park - located about 55 kilometres north-west of Flinders Island and approximately - the same distance from Wilsons Promontory in Victoria. Deal Island has an area of 1,576 hectares.
National priority area:	Coastal environments and critical aquatic habitats Community skills, knowledge and engagement
Funding:	$30,040 (2009-2011)
Partners:	Tasmanian Parks and Wildlife Service

Weed management, erosion control and revegetation on Deal Island

Project targets control of sea spurge, ragwort, slender thistle, and other weeds, stabilisation of eroding slopes, and restoration of natural vegetation while enhancing volunteer skills & capability.

Rising 305 metres out of the choppy Bass Strait are the steep cliffs of Deal Island, a 1575ha rugged, red granite island which is part of Tasmania’s most remote national park. It’s a difficult journey to Deal: by air to Flinders Island and then a four hour boat trip, if the Strait’s notorious sea conditions are fair. The insidious weed, sea spurge, however, arrives with ease by sea.

If left untreated, sea spurge could eventually invade the island’s tussock grassland. This threatens the island’s “biogeographically significant” status. Being situated half way between Tasmania’s Flinders Island and Wilsons Promontory on the mainland, the native flora is transitional between mainland and Tasmanian floras. Some 20 plants are listed under the state’s Threatened Species Protection Act 1995.

Fortunately, Deal Island has more than 100 friends. The truly dedicated volunteer group, Friends of Deal Island, runs two working bees a year with eight participants per visit. Transport costs for one working bee are about $7000 and delays due to bad weather are frequent, with a week-long wait not uncommon.

Since the injection of $30 040 from the Australian Government’s Caring for our Country initiative, four working bees have been held, all attended by lighthouse caretakers Bob and Penny Tyson.

“Anyone going to Deal Island has to have a sense of adventure,” Bob says. “We have spent three seasons getting to know Deal Island, its flora and fauna, the weeds and other threats... and falling under the spell of isolated island life.”

In keeping with the national priority areas - coastal environments and critical aquatic habitats, and community skills, knowledge and engagement - funds have engaged 100 people in the project, 45 doing hands-on work on the island and the rest participating in meetings, seminars and displays.

On-ground work focuses on reducing sea spurge, ragwort, slender thistle and other weed infestations by a combination of hand pulling and herbicide application by cut and paste and spraying, with careful removal of seedy material.

“Sea spurge is high priority for treatment because it is spreading through native vegetation and suppressing it,” Bob says. “If it spreads as far as some mainland infestations it could spread throughout most of the area currently occupied by tussock vegetation (20 per cent of the island). It also impacts on the Tasmanian listed rare plant coast twinleaf and inhibits its growth.”

Ragwort occurs as a 5 hectare main patch with several smaller outliers. In spring 2008 a previously unknown population of the Tasmanian-listed endangered orangetip fingers orchid was recorded on the edge of the infestation, increasing the urgency for its treatment.

Funding also enables volunteers to stabilise eroding slopes and restore natural vegetation. The steep slopes above East Cove have been degraded by a history of grazing, burning, and firewood collecting. Although these activities ceased with automation of the lighthouse in 1992, grazing and browsing by wallabies, brush possums and rabbits has prevented the return of healthy native vegetation.

Repair work includes: trial fencing to exclude grazing, installation of erosion bars and direct seeding and planting of she-oak, grey saltbush, bower spinach and tussock grass.

“Real progress is being made,” Bob reports. “The elimination of two weeds - marram grass and cumbungi - and the reduction of arum lily, both species of mullein, and horehound. There’s been a marked reduction in the area occupied by sea spurge and less than 1 hectare remaining at East Cove. Regular weeding of new seedlings will be needed for a few more years, then all that is needed to keep the island free of sea spurge is to patrol the beaches annually for any seedlings from seed newly washed ashore.”